Industrial plant facilities particularly chemical plants are large and complex systems which include chemical, mechanical and electrical equipment subsystems. An abnormal condition of operation or an impairment in any piece of equipment can cause a decrease in plant production or in the efficiency of plant operation or cause complete plant breakdown. Accordingly, it is essential to identify the fault as quickly as possible and to repair it. It is customary in the design of a chemical plant to include an instrumentation panel which may be located at the plant site to identify applicable alarm or shutdown conditions. The instrumentation panel contains a multiplicity of signal lights which are integrated into the chemical, mechanical and/or electrical equipment subsystems through control circuitry to respond to upsets corresponding to predetermined changes in process variables for identifying the existence of an abnormal condition of plant operation. A signal light functionally identifies an existing alarm or shutdown condition corresponding to each major equipment subsystem in the plant. The generation of an alarm or shutdown signal means only that one or more process variables which may be affected by a fault in the major equipment subsystem corresponding to the alarm or shutdown light has exceeded or dropped below a predetermined set point range. It does not specifically identify the fault or give any clue as to the specific equipment component(s) that may have failed, the extent of the failure or how to proceed to evaluate the failure and take remedial action. This is relegated to the technician who has the responsibility for diagnosing alarm or shutdown conditions. In addition to the display of an alarm or shutdown condition electronic means may also be used to store the alarm or shutdown signal in computer memory and provide computer sound signals to alert operations personnel and/or to send such signals via modem to service personnel at a remote site.
To assist the technician to troubleshoot an alarm or shutdown condition many industrial companies commonly publish operation manuals which contain troubleshooting guides. These guides include lists of potential faults, usually in tabular form, as well as brief descriptions of anticipated symptoms, possible causes and recommended remedial solutions. Cross references are made to other sections of the same document, to sections of other publications such as vendor literature and to specific drawings located in a drawing package for additional information. Unfortunately once an alarm or shutdown condition occurs time is of the essence to determine the fault causing the alarm or plant shutdown and to correct it. The technician simply does not have the leisure of spare time to pursue an exhaustive search through various cross reference leads as set forth in the operations manual to troubleshoot an existing plant alarm condition. Moreover the technician is under such tension to resolve the alarm or shutdown condition that looking at reference material is not always considered productive. In any event the references identified in a troubleshooting guide refer to various information sources and are not coordinated for the technician to use in connection with the resolution of a specific alarm or shutdown condition the cause of which is precisely what the technician needs to diagnose.
In recent years diagnostic expert systems have become available in which use is made of "if-then" rules to represent the heuristics of selected human experts on any given subject for use as a diagnostic tool. The if-then rules may be encoded from knowledge acquired from selected human experts in knowledge acquisition sessions conducted specifically for preserving the valuable heuristics gained and perfected over the years for diagnosing plant equipment and process faults. Knowledge may also be gleaned from supporting materials such as operations manual, vendor literature, training course notes, flow charts, fault tree logic diagrams and other such technical documents to create the if-then rules, which are complied to create a rule-based expert system. Typically, such an expert system utilizes multiple choice questions asked of the operator to identify observable symptoms of known faults. If electronic means are available to automatically acquire and input certain plant process data into the expert system then the operator or service technician is expected to answer mutiple choice questions to supplement the information automatically gathered. The expert system follows a predetermined inference sequence (e.g., backward chaining and/or forward chaining) in processing the rules and upon identification of a problem, in response to the information contained in the acquired process data and/or to the information contained in the operators answers to the multiple choice questions, is able to formulate a probable answer for the real cause of the process or equipment fault under consideration followed by advice for remedial action. The quality of the advice produced by a rule based diagnostic expert system depends heavily upon the quality of knowledge which can be attained by translating the diagnostic expertise of a human expert into a set of discrete rules to enable the expert system to identify the problem using the information contained in the gathered plant process data and/or that supplied by the service technician. Accordingly the operator is not an active decision maker in evaluating the available information to diagnose the problem and is not offered an opportunity to engage in active learning in the review of the available symptoms or in validating suspected faults or in selecting the appropriate remedial action. Moreover, if the queries of the expert system are not adequately or properly satisfied the diagnostic expert system will produce non-conclusive and/or useless advice or if an excessive number of questions are asked of the service technician, many of which do not have easy answers, the service technician is likely to be frustrated. Expert systems tend to be resented over time because decision making is excluded from the operator and the operator gains little if any experience from its use.